Sciences : histoire orale

ARRIBART Hervé, 2001-02-19, 05-29, 02-20

Sophie Jourdin — 2011-06-16T07:31:17Z

Hervé Arribart is the Scientific Director of Saint-Gobain Recherche, an international company of French origin with an emphasis on glass manufacture. He took his PhD from the Ecole Polytechnique in Paris in the mid-1970s and subsequently researched ionic transport using nuclear magnetic resonance. In the late 1970s he worked with Jean Rouxel's group at the University of Nantes. In 1981 he joined the company Elf to work in research and development. In 1985 he moved to Saint-Gobain, where at first a large portion of his research was closely related to the practical problems of production. In 1990 he started a laboratory (a joint venture of Saint-Gobain and the CNRS) on the basic science of glass surfaces, using a diverse set of tools and especially the Atomic Force Microscope. In 1999 he moved to the more managerial position of Scientific Director. Hervé is also on the staff of this project.

2001-02-19 :

HERVE ARRIBART (HA) : I studied at the École Polytechnique in Paris. The selection to the school is done mainly on mathematics. But during my studies I learnt to appreciate physics in particular. I decided to pursue research in solid-state physics. It was a good place to study physics. While in my last year as an undergraduate I did a Diplome d'Étude Approfondie in parallel (an intermediary between an M.Sc. and a PhD typically done for a year before starting one's PhD studies). In Orsay, near the École Polytechnique, there is a very famous place in solid state physics, a lab started by Jacques Friedel - a great name in solid-state physics. I followed this course and afterwards I did the PhD at the École Polytechnique in the field of condensed matter physics. In principle I ought to have started with a topic distant from materials science. I extracted spin-polarized electrons from semiconductors. This was in 1974.

ARNE HESSENBRUCH (AH) : How did one extract spin-polarized electrons in 1974 ?

HA : It is true of all solids, but in semiconductors it is especially interesting that when light falls upon a surface there is a coupling between the spin of photons (in classical physics : the polarization of light) and the spin of electrons. Electrons in the upper layer absorb light photons depending upon the spin. If by some technique you can extract electrons from the conduction band of the semiconductor, you can find ways to select electrons of specific spins. This was quite important at the time because at big-science institutions such as LEP [Large Electron Positron collider] or SLAC [Stanford Linear Accelerator Center], there was a need for spin-polarized electrons. And of course you then needed solid-state physics to do it. But the man who in principle was my supervisor decided to do something else. His name is Claude Weisbuch, and he is now a good friend of mine. For a few years he was the scientific director of the French Department of Defense. He is still working in solid-state physics, in the optics of semiconductors. But he decided to do something else and Bernard Sapoval, another professor at the lab, proposed that I work on new materials. At that time there was little contact between solid-state physics and solid-state chemistry. The idea was to link up with chemists. This is why very early on in my career I had contact with chemists. We worked with Parisian solid state chemists on a new material. We found a new way to draw single crystals of an already existing material. It was very nice because we could examine transport and NMR phenomena. And the material, a copper vanadium sulfide exhibited astonishing properties : a large spread of conductivity that one can measure in a standard experiment. We suspected that this was due to mixed conduction properties. Mixed conductivity refers to conductivity by both electrons and ions. The experiment appeared to verify our a priori suspicion. This gave me the possibility to present a model for mixed conduction in this material and to understand the influence of ion transport and electron transport. I also used NMR in order to understand which ions moved. It turned out that the copper ions moved. So, this was the subject of my first thesis. At the time, in France, there were two theses. The first one was called "thèse de troisième cycle". The second was the "Docteur es sciences". This degree does not exist any longer. The thesis that is done now is shorter.

I decided to continue to work with chemists. I decided to combine NMR and transport measurements. I changed my collaborators, turning to two different groups. In my PhD there had been two chapters on NMR. But I wanted to study proton transport. I had two reasons. One was that protons give a strong NMR signal. The second reason was that two reasons had been given for proton transport. In one, protons move in individual jumps. In the other the proton is a part of a more complex molecule such as the ammonium ion (NH4+) or hydroxonium (H30+). In the former case we can see the transport phenomenon as a result of molecule rotation and proton jump. The molecule would turn and the proton jumps to the neighboring molecule, which again turns and so on. This was called the rotation-jump model. The second model was for the whole complex ion to jump. This was called the vehicle model because the whole molecule acts as a vehicle. So I worked with one group of chemists in Nantes, at the Institut de Matériaux de l'Université de Nantes. It had just been created by Jean Rouxel, a chemist. With them I worked on a substance called antimony acid - a solid. I was able to show using NMR that transport occurred in this case with rotation-jump. Protons used H30+ as a complex rotator. I was also able to show that the jump was due to quantum mechanics within a certain temperature range. It was not the usual ion transport of classical mechanics.

AH : A tunneling effect ?

HA : Yes, this is one aspect of protons, because protons are very light ions allowing for this quantum effect. The other material I studied was ammonium beta alumina. This was the standard beta aluminium in which the sodium had been ion exchanged with ammonium. This material was very interesting from the perspective of NMR. All kinds of ionic motion took place at different temperatures. At the lowest temperatures, that of liquid helium (1-4K), there was rotational quantum motion. As the temperature increases the motion becomes classical.

AH : If I may make a comparison with Stanley Whittingham here. You were working on some of the same materials, you were using some of the same tools (NMR), but you were asking very different questions, right ?

HA : Yes, that is true. I was not at all involved in the application. For two reasons : French chemists were interested in materials and did not look to the application. And chemists were between me and the application, so I had no contact with attitudes such as Whittingham's. I was very happy working on the solid-state physics problems.

AH : And we are talking about the late 1970s now ?

HA : Yes, I began the proton transport research, I think, in 1976.

AH : And it went on for how long ?

HA : For five or six years.

AH : And you lived in Nantes ?

HA : No, I remained in Paris while collaborating with the Nantes group.

AH : Were you employed in Nantes ?

HA : No, not at all. At the beginning I was employed at the Ecole Polytechnique as a research assistant, and then I was hired by the CNRS - in 1977.

AH : So, the CNRS paid your salary, you were able to do basically whatever you wanted, and you collaborated with Jean Rouxel and coworkers because you found it interesting ?

HA : Yes. It was a chance to work with an outstanding chemist. French chemists were really very good. The problem, as we just said, was that there was little interest in application.

AH : What did you do next ?

HA : After my PhD thesis, I found it interesting to go to industry.

AH : I imagine that there were many advantages and disadvantages to leaving academia for industry. For instance, where was status greater, what paid better, where were working conditions better ?

HA : First of all, it was rare, even more so than today, for CNRS people, or people within the public system, to go to industry. I cannot give you a clear answer about my motivation - it was not even clear to myself at the time. I did get a higher salary in industry. I also had personal reasons for leaving Paris and going to the Elf company. I went to an Elf research lab in the Southwest of France, in a very nice place in the Pyrénées. I had small children at the time and it was much better for them to grow up in the countryside and in a very nice climate. I was also curious. So the decision involved many elements. And anyway, it was not irreversible. The CNRS allowed me to take a three-year leave after which I could have gone back. With regard to the working conditions : I was of course less free than I had been at the CNRS, but I found it more stimulating because there were a lot of different problems on the horizon, arriving almost every day. We could easily get the necessary equipment at the CNRS and at Elf, so there were no differences there.

AH : The restrictions at Elf had to do with what you were allowed to study ?

HA : Yes.

AH : What did Elf want you to do ?

HA : In principle I was hired to work on solid-state sensors. Because it was not in the direct line of my previous work I proposed that I work on solid-state sensors and ion conduction. We developed a family of sensors named ISFETs (Ion Sensitive Field Effect Transistors). It was a new kind of transistor at the time but now it is very common. You control the electrode using field effects, opening and closing the circuit between the two other electrodes. This is the way the transistor works. My idea - not an original one - was to replace this way of controlling the electrode, the gate, to replace it with a membrane, selective to such and such an ion. If you put the device in a solution containing the ion for which you have designed the system, the membrane will be charged. This charge will change the state of the solid-state transistor. It worked all right for protons. We could use the device to measure pH and afterwards we just had to change the nature of the membrane, choosing a different solid electrolyte, such as calcium fluoride.

AH : Your toolkit remained the same and you still used NMR ?

HA : Not NMR, but yes. You need large samples in order to do NMR. So it was mainly electrochemistry and surface analysis. This was between 1982 and 1985. But as I told you, in industry new projects can arrive almost every day. I had developed some skills in electronics using instrumentation at the École Polytechnique. Elf applied for a patent for a medical analysis system, a small instrument to be sold to private practitioners, as opposed to hospitals. This had nothing to do with solid-state ionics. But the people working on this project needed someone who knew about electronics, and so I got progressively more involved. After one or two years it had become my main project. This worked very well. I was very proud to design an electronic system that required no manual setting. It was set in the factory forever. This was a critical issue, because we thought that doctors could not be expected to deal with electronics - and I am sure that we were right in this. So there was nothing to check or calibrate - the system was self-calibrating. So it worked very well, and after only two or three years Elf built a plant and people were hired. But in 1984 and 1985 there were big changes in chemistry. And there was a great redistribution of all chemical industries. And Elf, that had been an oil company, in this period expanded to become also a chemical company. As a result a lot of the more diversified lines of business lost in importance. Many projects like ours were discontinued. But because we were already quite advanced we found a way to keep going. In fact it was Dupont de Nemours that found that our system was complimentary to some of theirs. The result was that Elf shipped the patent and everything else to Dupont. For a few months I considered following the project to Dupont and to the United States. In the end I decided against. I still wanted to work in solid-state physics and not to work completely in the instrument making business. But for one or two years I continued as a consultant.

2000-05-29 :

HA : For both personal and professional reasons, I decided to stay in Paris, and then Saint-Gobain offered me a position, working in a new research field : polymer adhesion on glass and other materials. It was a new topic for me too. At the time adhesion was not even considered a science. It was before Pierre-Gilles de Gennes's Nobel Prize in polymer adhesion [1991]. It was rather considered an art. Even though I had no background in the field I was interested. What interested me in the Saint-Gobain proposal was that real breakthroughs were to be expected in the science of adhesion when two materials are brought into contact. In fact this was my first real industrial experience. Of course CNRS had not been an industrial experience at all, and even at Elf I was always in the research lab. As I explained, my work at Elf had nothing to do with the industrial activities. I never visited factories. At Saint-Gobain I had to do this, at least in the beginning.

AH : Did you not say that your development of the medical analysis system resulted in the setting up of a plant ?

HA : Yes. I did participate in the design of the plan, in order to make it efficient. But I had no role in the plant itself after construction. It was also a small plant for high-tech activity.

AH : You had nothing to do with the fabrication side of it, situated in the plant – merely the R&D before the plant became functional ?

HA : Yes, exactly. Saint-Gobain of course has many plants all over France and Europe, and even the United States. But at that time, the company was still franco-français [French through and through] in its general spirit and culture, despite the many factories in other countries. There were only French directors and the system was based on the French system of education. There is a hierarchy from the École Polytechnique through the École des Mines and the École Centrale to lesser schools, and you carry the status of your school within you for the rest of your life. I remember that I strongly felt the weight of tradition when I first joined the company. It is true that winds of change were already blowing then, but they were barely noticeable and needed a couple of years before really expressing themselves. But eventually the company changed its culture, and now the company considers itself an international one. I think a deep change has taken place during my 15 years with the company.

So, anyway, this was the first time I gained experience of the industrial aspect of research. My first task was to examine and synthesize different kinds of adhesion in Saint-Gobain's products and processes. I decided to simultaneously pursue fundamental reflection and a practical approach, helping the factories improve their processes. This was a very instructive experience. I learnt many things although I am not sure that I helped the factories all that much. I certainly learnt for myself that I preferred to stay within R&D and not to progress into production. On the fundamental side, I developed a network of contacts in public labs in France and the US. This became useful later on. After three years in the field, and having created a small research lab, I decided to gain some distance from the practical aspect of my work. It was also obvious to me that fundamental research was required first. Progressively the idea came to me to propose the creation a special laboratory dedicated to the basic aspects of polymer adhesion - and of course also to related issues such as the surface science of glass. But I knew that Saint-Gobain was not ready to have a laboratory for basic science by itself, so my idea was to set up a lab jointly with the CNRS. This was in 1988. From the administrative point of view this was feasible : a number of such joint ventures already existed, an example of which is Rhône-Poulenc. Of course I had to convince both Saint-Gobain and the CNRS of the utility of the project which was not straightforward. Although I managed to convince Saint-Gobain in a manner of hours, CNRS needed more prompting.

AH : Would you explain the nature of Saint-Gobain's research before your proposed laboratory ?

HA : It was a quite common kind of R&D geared towards problem solving. Helping the development of new products and solving problems within production.

AH : So the research agenda was driven by questions arising out of production ?

HA : Yes, and my idea was to get a more fundamental understanding of the questions which would enable us to help with such questions in a much better way.

Figure 1. Saint-Gobain Recherche, Paris

At Saint-Gobain I had to sell the idea primarily to the Vice-President of R&D. He took the decision just before retiring. The CNRS process was more complex. It has a democratic organization where decisions are taken by committees. The members consist of both elected researchers and individuals named by the Ministry of Research. They are divided up into different scientific sections. So here I had to convince a diverse group of people, and not just one person, as at Saint-Gobain. As I mentioned, I had developed a network of relationships in the fields of adhesion and surface science and now this turned out to be useful. I knew that many people approved of my research agenda. My project was accepted without much fanfare, but it still took a while because of the administrational hoops that a proposal has to jump through within the CNRS. They meet only twice a year, and every decision has to be validated by the CNRS directors and so on. It took maybe 12 months. The laboratory started on January 1, 1990. But there was only a building and neither instruments nor people.

Figure 2. Joint lab : Saint-Gobain Recherche & CNRS

The three yellow arrows point to the units of the joint lab within the Saint-Gobain Recherche building.

In the meantime I conferred with scientists in many other labs trying to recruit people. Of course the CNRS could not order people to go, so I had to entice scientists away. I estimated that I needed three scientists from the CNRS in addition to three scientists from Saint-Gobain. Two of the latter had already worked with me, and they followed me to the new project. A further researcher came from somewhere else – it was a young Chinese woman. We also had two or three technicians and some PhD students. Altogether, it took a year or so to gather everyone together. We also had to buy instruments and the process of getting the laboratory shipshape lasted altogether something like 2 years. We began to actually do some research in late 1990. And from then on the activities progressed rapidly. In two to three years we reached a plateau of 20 people, a level that had been stipulated by the CNRS. A third of the people had come from the CNRS, a third from Saint-Gobain, with PhD students constituting the last third.

AH : Where did they come from ?

HA : The latter were doing industrial PhDs (Contrat à Durée Déterminée) with Saint-Gobain, and their salary came jointly from the French Ministry of Research and from Saint-Gobain. Of the entire staff, about half each came from chemistry and physics. It was crucial that we develop knowledge and expertise in both these fields. Later we also developed an interest in mechanical problems.

Figure 3. The SPM from Park Scientif Instrument

AH : What was the instrumentation ?

HA : There was a conjunction of the beginning of our lab with the very early days of scanning probe microscopy. This new kind of instrumentation offered a very exciting opportunity. There was a risk in this. We purchased the first Atomic Force Microscope (AFM) ever in France. We bought it from Park Scientific Instruments. Later we built the first AFM for UHV purposes. There were many people then who thought the instrument had no future, so it was a risk to invest time and money in it.

AH : Why did people think it had no future ?

HA : The objection was that it was not clear that atomic resolution could actually be achieved with the AFM. It was not until 1993 that Binnig showed true atomic resolution.

AH : Well, yes, but before he had claimed to achieve atomic resolution. In 1993 he only claimed that so far he had been mistaken and only in 1993 did he achieve true resolution. Is that not right ?

HA : Yes. But in 1993 the community was convinced. The reason I did not hesitate was that atomic resolution was not actually the big issue for our purposes. Even a resolution of 1 nanometer amounted to a great deal. Much could be done with such a resolution in the field of adhesion, and also in fracture mechanics and surface chemistry.

AH : I have the impression that since 1995 or so many people argue that atomic resolution is not really that important, and that in the early 1990s it was still considered the holy grail. So you were unusual in that you had this attitude so early ?

HA : You are right that atomic resolution had a special ring to it in those days.

AH : Did you emphasize the issue of atomic resolution in your application to the CNRS ?

HA : I am not sure. Even today, nobody has achieved atomic resolution in glass. So it would have been a hard sell, also then. The same goes for polymers. And those two were our substances under investigation.
There is a difference between STM and AFM. They obey two different logics. The STM has remained a tool of basic research, in surface science. The AFM, even early on (and this would be interesting to discuss with Calvin Quate or Gerd Binnig), there was a hope that it could be useful, for example in other fields of science, such as mine, or in technology, such as process control, microelectronics, semiconductors, and so on. Generally speaking, in early phases there are always many people who think that a novelty will never become common. We have to remember that in 1987 or 1988 solid probe microscopes were still big and unwieldy instruments. Of course miniaturization had set in by 1990, but it was a novelty. Only very few people were convinced that the AFM would become so common. Calvin Quate is one of the few. The STM has revolutionized basic research on metals and semiconductors. There was a reaction against it, because surface science was done using diffraction techniques working in reciprocal space. Surface scientists were formed in this mode of research. They resisted the change, feeling that newcomers would enter their field without the kind of abstraction that had hitherto been key to access to the field. Working in ordinary space was too easy ! Of course it has not actually become easy because the instrument has brought its own problems, and there are still people working with diffraction and in reciprocal space. The two complement each other.

AH : So this is the background against which your decision has to be seen. You went out on a limb.

HA : Yes. The beginning of my lab coincided with the first commercial scanning probe microscopes (SPMs). We had to grasp the opportunity.

AH : How did you know about the AFM ? Was it a very visible instrument at the time ?

HA : No. I knew about it from publications, but in order to actually see an instrument, I had to travel to California - although I guess I could have seen one at IBM Zurich. There was an STM at Marseille, because two physicists there (Salvan and Humbert) had worked at IBM Zurich, and they had brought one back with them. But they had no experience with the AFM. So I went to the US and visited the very few labs with AFM, both academic labs and the start-up companies of PSI [Park Scientific Instruments] and DI [Digital Instruments]. At Stanford University I met Calvin Quate and at UC Santa Barbara I met Paul Hansma.

AH : Was there a relationship between Paul Hansma and DI ?

HA : I don't remember. But at any rate it was not as close as the one between Quate and Park. I think Park was a former student of Quate's.

AH : So you purchased an AFM from Park. What about the other kinds of instrumentation you purchased for your lab ?

HA : Yes, we had to get other instruments, partly because it took a long time for the AFM to arrive. I had to go to the US to compare the DI and the Park instruments, and I discussed it with the physicists and chemists in our lab before ordering, and then we had to wait for the delivery – maybe 4 months or so. We got a 40% discount, because we were the first French customers, and they hoped that we would open the French market for them. I had very good discussions with Quate, and I think he trusted me to be a good advertisement for him in France. I think we paid 400,000 French Francs, so that the catalogue price was in the order of 800,000 French Francs [approximately US$100,000].

We bought also an infra-red spectrometer, in order to study molecular grafting on oxides. This we used as a complement to the AFM. And as I said in a previous part of the interview, our approach was to combine the traditional surface science (very clean surfaces) with “true surfaces” interacting with the environment. The infra-red spectrometer, XPS (X-ray Photoelectron Spectroscopy), and LEED (Low-Energy Electron Diffraction) were good tools for the traditional surface science approach working in UHV Ultra-High Vacuum). And also HR-EELS (High-Resolution Electron Energy Loss Spectroscopy). Our choice was risky, but it turned out to be correct. Our decision to build bridges between the two approaches was taken in 1992 or 1993. Quite early on in our project we built a surface force apparatus (SFA). It is not at all an AFM – there is no concept of high resolution, but it is similar in that you can get a direct measurement of the force interacting between two objects only a few Ångstroms apart. The idea is to make the measurement quantitative in order to study whether the interaction is due to van der Waals or electrostatic forces. In fact this project took six years – not for technical reasons but simply because we had to get the right people.

AH : Each instrument had its strengths and weaknesses in terms of resolution and the scale of the surface analyzed. And each instrument required special skills. The AFM, for example, requires quite some expertise to disentangle signal from instrumental artifacts, right ?

HA : Yes, artefacts were a real concern at the beginning, when we all had very limited experience. We had to pay much attention in order to ascertain the results.

AH : Can you explain how one separates signal from artefact ?

HA : There are different kinds of artefact. One that now seems quite natural but was hard to understand then is the tip effect. If the surface under examination has sharper topographic features than the tip, then the tip will be imaged rather than the surface. We had trouble with this kind of artefact. In fact, when studying tin oxide deposits on some substrate we got very nice images that we at first interpreted as small crystals having the similar orientation. We were very excited to find a growth mechanism of specific orientations on isotropic surfaces such as glass. I decided to present this result at a small meeting in Davos, Switzerland. The topic there was in fact “The AFM for Technological Applications”. Famous scientists attended, including Calvin Quate, Jim Gimzewski, and Heinrich Rohrer. There were only some 10 people there, because this was very early, maybe 1991. The night before my presentation, I began to wonder that the result was really too beautiful to be true. I telephoned my lab and asked people there to turn the sample by some angle and do the experiment again. That way, the features should have changed if they belonged to the surface. But they did not, and so we knew that the features belonged to the tip. So I did not present that particular slide in my talk.

AH : So rotating the sample by some degree is one way of identifying artefacts.

HA : Yes, that will eliminate this kind of artefact, the tip effect. There are also adhesion artefacts, some of which have been solved in the meantime thanks to new recording techniques such as the tapping mode.

AH : Digital Instruments has a patent for the tapping mode, right ?

HA : Yes.

AH : So the Park instrument that you bought did not have the tapping mode ?

HA : No it did not. The tapping mode did not become available until 1993 or so. Later on, Park Scientific Instruments did do something similar, but they may not call it tapping mode. The DI patent covers the name. And in the straightforward contact mode many artefacts were possible ; for example when looking at soft materials and polymers surface scratches easily occur. If you do that you image the substrate only. One way to identify this effect is to scan again with a smaller tip-surface interaction. In some cases you will find miniature small squares where the surface had been damaged in the course of the first scan. Some artefacts are very common, others are quite specific and harder to identify.

AH : In what you have explained, the identification of artefacts is internal to the instrument itself. It is not that you can go and compare the results of an AFM scan with those from a different instrument ?

HA : You can change the tip, and you should identify artefacts unless you are very unlucky to get the same tip. Everybody understood that the AFM has great potential not just as an imaging instrument but also to measure adhesion, hardness and so on.

AH : Using force-distance curves ?

HA : Yes, force-distance curves. This turned out to be very useful for us. For instance in order to understand the electrostatic interaction between oxide and a silicon nitride tip under water. This was original work. For example, in polymer adhesion we checked if it stayed on the substrate and what scratching would do. Of course such ideas were floating around at the time.

AH : Were you important to the subsequent spread of the AFM in France ?

HA : Yes, people came to our lab. Another lab, at the Institut Curie, that got an AFM at almost the same time. For a while we were a small community but then gradually we grew larger and larger. Yes, we were the pioneers. It was exciting.

2001-02-20 :

HA : I went with one of my sons who was 11 years old at the time to see Park Scientific Instruments. There were no more than 10 people working there, in fact I think it was more like three. It was very small and familial. We discussed and had tea. I enjoyed discussing with these people. It was nothing like an established company.

AH : What did it look like ? Did they work out of a garage ?

HA : Something like between a home and a garage. It was a small house. Even Digital Instruments started out like this. Already in those days DI, and especially Virgil Elings, was much more commercially aggressive, but they were very small too at the time.

AH : Did you stay in touch with some of these guys ?

HA : I stayed in touch with Calvin Quate for five or six years, until 1996. After that I lost the contact but he will probably remember me because we had many discussions. It was curious to see his impact upon materials science. In fact it was very difficult for him to get the first paper on the AFM accepted in Physical Review Letters. Some of it was considered just a pure mechanical profilometer. It had good resolution but it was not really anything new. His project now is very interesting from what I can tell reading his articles in the scientific journals. And he really is a very nice person. Maybe the last time I saw him is when I invited him to give a talk at Saint-Gobain Recherche.

AH : So you stayed in touch with him in the early 1990s, while you were developing your own AFM. I guess the use of the AFM changed the project from what you had originally envisaged ? Did you continue using all the other tools or did you focus exclusively on the AFM ?

HA : We used the other tools.

AH : What did you buy for your laboratory ?

HA : Infrared spectrometer, XPS, HR-EELS (High Resolution Electron Energy Loss Spectrometer), LEED. Quite quickly we had three AFMs. I wanted to develop a PSTM working in the infrared but unfortunately that particular project died because the physicist we had working on it left.

AH : What journals show the history of these instruments best ?

HA : In the beginning it was mainly in the general physics journals such as Applied Physics, Applied Physics Letters, Physical Review Letters, Surface Science. Now there are specialized journals. A journal like Journal of Scientific Instruments is not so important in this respect. Langmuir is also important for soft matter.

AH : Do any of these journals have review articles ?

HA : I am almost sure that all of them do.

AH : We were talking about the various instruments you had in your lab. How did you apply them to your research project ?

HA : The idea was to have two parallel approaches. We were mainly interested in adhesion, molecular grafting and so on. One approach is the classical view of surface science, the ideal surface approach. The other is the REAL surface approach, taking the environment as a part of the system.

AH : Not working in Ultra-High Vacuum (UHV) ?

HA : Yes. But we were trying to make the two approaches meet.

AH : So when you started working with the AFM in UHV, the point was to simplify the experiment ?

HA : Yes.

Figure 4. UHV Chamber et AFM in UHV Chamber

If a probe were to be introduced directly into the UHV chamber, it would take days of pumping to achieve UHV. Instead, it is first introduced into an antechamber, whereupon a vacuum is produced there. Only then can walls be opened without reducing the UHV too much. By pushing the rods labelled 1 and 2, the sample is transported in successive stages into the central chamber. Several instruments are attached to the chamber, including an XPS. On the right, an AFM can be discerned in the UHV chamber.

AH : How did the various instruments complement each other ?

HA : The spectrometers provided structural information. They give a chemical signature. One point of interest was silver on magnesium oxide. In order to have a simple model of glass we chose to study this problem within pure single crystal. We had the probe in situ in the same UHV chamber where we had the instruments to add the deposition techniques. In the case of silver it was just thermal evaporation. We wanted in situ real-time studies of the atoms arriving upon the substrate, the oxide surface. There were two models in this problem. One was that the atoms remain isolated or form small islands, so that the growth process is two-dimensional, so that you first get a perfect monolayer before a second layer is started upon. The other is that growth is three-dimensional with occasional collapses into flatness. To study this it is of course useful both to look directly and to use diffraction techniques. But in order to understand the process you need to grasp the interaction between the silver and the oxide. And only spectroscopic techniques will help here. We always tried to look at a problem from two differing points of view – in this case geometrical and chemical.

AH : You make it sound easy. You just use one tool and you get the topography, and then you use another and you get the chemical composition.

HA : Well of course it is not at all easy. It was very difficult because for instance, the STM works very well when you have a smooth surface but when you have corrugation it becomes much more difficult, because this corrugation interferes with the instrument. In spectroscopy you integrate over the size of the beam which is much larger than the surface scanned by the AFM. So you have to do many different experiments to see what effect the temperature has and so on. You also have to model the interaction. This was a little known problem. What is the mechanism of very small silver clusters on magnesium oxide with other silver clusters in the neighborhood ? It was a new problem. So it took time to understand the system.

AH : What is the measure of success ? It was partly CNRS, so you were under pressure to publish ?

HA : Yes.

AH : And since it was partly Saint-Gobain you had to get patents ?

HA : We had to do both. It was an interesting exercise in communication. In my position as head of the lab, I could not use the same words, the same way of presenting things when addressing different audiences. From time to time it was necessary to gather the scientific and the industrial people together under one roof.

AH : And what language did you speak then ?

HA : Fortunately everyone was happy with this lab, so it was not quite so difficult. The conditions were good. Nonetheless your question is quite correct. It was interesting.

AH : How did you convince Saint-Gobain that this would have a pay-off ? And how did you negotiate long- and short-term goals ?

HA : The short term was a problem. It was not straightforward to plan a new product for the company. The pay-off was very diffuse and difficult to identify. One way of motivating the directors was the argument that we trained very good PhD researchers for Saint-Gobain. And this was not expensive for Saint-Gobain, because they shared all the expenses with CNRS. Up until now this has not been a problem.

AH : Stanley Whittingham told me that in the last 15 years or so there has been a tremendous shift in company planning towards the short term in industry. Partly this was due to the MBA education and the fanning out of this new generation of business administrators into all nooks and crannies of industry. As a result the long-term disappeared, because everything had to fit into the financial year so that you have something to show to your shareholders.

HA : It is true that this has taken hold in industry. We had the good fortune that it was not very developed in Saint-Gobain. But also, the time required for the development of new glass materials just is acknowledged to be greater than that in electronics or informatics. When we start new projects, we are simply not able to show a product six months later. So we are less exposed than people in other fields, but the general development that you alluded to certainly has taken place. Maybe our situation will also change in the future. We may be excessive.

AH : Has the accountancy changed for you ? Did you have to write annual reports ? And has it changed over the last ten years ?

HA : In general ?

AH : Well, for the CNRS I can sort of imagine it. In academia you would specify the number of publications that you have produced and that is the measure. End of story. And that is very simple accountancy. But if you account to a company, keeping in mind the increasing influence of MBAs : did you have to account for your expenses in ever greater detail ?

HA : I do not think there has been such a change in the last decade.

AH : And do you write annual reports ?

HA : Bi-annual. But I am not in this lab anymore ; I left two years ago.

AH : Okay, so during the 1990s up until two years ago you wrote biannual reports to the company and in that period the structure of the reports did not change.

HA : That is correct.

AH : Did you have to specify just how much money you spent ?

HA : Yes, but also there, no change took place. And I always reported to the same person within Saint-Gobain. He was basically content with what we did, so it was never critical. It is true, it might have changed with a different person in charge.

AH : So, how did the instrumentation change throughout the 1990s ? The AFM became commercially available to an ever greater extent, you were able to buy many more things off the shelf. Is that true also of all the other instruments ?

HA : Yes, there are different aspects to your question. We used to build many instruments ourselves, and this was of great use for training. And this has changed. A reason the French PhD has been shortened is that equipment is being bought and not made in-house. That is a general trend. Science is changing as a result, because using a commercial instrument is not the same. When you develop an instrument yourself you know exactly how to get the result. In the specific case of AFM/STM : probably the AFM has been developed much more than the STM. In the STM the major breakthrough was with the driver and that was quite early. I think it was possible to purchase an STM driver already by 1992. Variable temperature was a little more difficult, but it was certainly available by 1994. Different ways of scanning and acquiring information were developed. Otherwise the evolution was purely technical : cheaper, and more diverse (such as an STM expressly for electrochemical research). By contrast the AFM has developed rapidly. Tapping mode and other modes where you measure not only the distance but also hardness, conductivity, adhesion, chemistry. It has become possible to map all these parameters. This explains why more and more people use the AFM.

AH : It has also become cheaper, right ?

HA : Yes.

AH : It has certainly become more user-friendly, adaptable to different circumstances.

HA : Yes. For the STM : there have very beautiful studies made of the coupling between tunneling and modulation. You might modulate the tunneling current with light for instance. You can even leverage the spin of the tunneling electrons. So you can do beautiful physics. But this contributes little to the democratization of the technique.

AH : I have the sense that Calvin Quate, by contrast, is working hard to increase throughput.

HA : Yes, that is right. There can be two reasons for doing that. To make the investigated part of the surface larger – of use in the semiconductor industry. And to shorten the time required for a scan. He is trying to use the system technologically.

AH : Okay. Two years ago you left your lab. Your own lab. Why ?

HA : I wanted to try something new and I was lucky to find someone who was well capable of taking over and for whom I have a lot of respect. He is from a different background. So now it is a different group. I became the Scientific Director of Saint-Gobain Recherche. There are two parts to the job ; one is to be the scientific manager, the other is to establish contacts in the outside world, and to promote innovations within the company, for instance with the marketing people.

AH : You were promoted ?

HA : Yes.

AH : And you have become slightly removed from lab work ?

HA : Yes, completely, I am now involved in organizational work.

AH : In fact, our project resembles your job in the sense that we stand back and look at the scientific research and try to gain a perspective ?

HA : Yes, you could say that.

Fin de l'enregistrement

Pour citer l'entretien :

« Entretien avec Hervé Arribart », par Arne Hessenbruch, 19 février, 29 mai et 20 février 2001, Sciences : histoire orale, /spip.php ?article47.

Pour citer l'entretien :

« Entretien avec Hervé Arribart », par Arne Hessenbruch, 19 février, 29 mai et 20 février 2001, Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article47.

Lieu : dans le salon (les 19 février et 29 mai 2001) et dans la petite salle de réunion (le 20 février 2001) du Dibner Institute, Etats-Unis.

Support : enregistrement sur cassette.

Transcription : Arne Hessenbruch.

Édition en ligne : Sophie Jourdin, Sacha Loeve.

DE GENNES Pierre-Gilles, 2002-05-02

Sophie Jourdin — 2011-06-15T20:52:04Z

Pierre-Gilles De Gennes (October 24, 1932, Paris – May 18, 2007, Orsay) was a French physicist and the Nobel Prize laureate in physics in 1991. He was Director of the École Supérieure de Physique et de Chimie Industrielles de la ville de Paris (ESPCI ParisTech) from 1976 to 2002.

He majored from the Ecole normale supérieure in 1955 and took his PhD in 1957. From 1955 to 1959, he was a research engineer at the Atomic Energy Commission (CEA) in Saclay, working on neutron scattering and magnetism. During 1959, he was post-doctoral visitor with C. Kittel at Berkeley. When he became assistant professor at Orsay in 1961, he started a group on superconductors and authored The Superconductivity of Metals and Alloys (W.A. Benjamin, New York, Amsterdam,1966). In 1968 De Gennes switched to liquid crystals and published The Physics of Liquid Crystals (1974). Meanwhile, he became a Professor at the Collège de France in 1971 and started a collaborative research on polymer physics with Strasbourg and Saclay. The joint project became known as STRASACOL (Strasbourg-Saclay-Collège de France). De Gennes' contributions to this domain are described in Scaling Concepts in Polymer Physics, published in 1979. Since 1976, De Gennes has been the Director of the École Supérieure de Physique et de Chimie Industrielles. In 1984, De Gennes turned his attention to interfacial problems, in particular in the dynamics of wetting. His research group – Françoise Brochard, Jean-François Joanny, Jean-Marc Di Meglio, D. Quéré – defined general laws of wetting and dewetting which are of great interest for practical applications. In 1989, De Gennes entered a new field, the physical chemistry of adhesives and became the champion of “soft-condensed matter physics”. In the late 1990s he started working on the design of artificial muscles with the Institut Curie. AT the time of the interview (2002), he was concerned with cellular adhesion.
De Gennes has received a number of honors and medals all over the world in addition to the Physics Nobel Prize in 1991 “for discovering that methods developed for studying order phenomena in simple systems can be generalized to more complex forms of matter, in particular to liquid crystals and polymers”. He is a member of the French Academy of Sciences, the French Academy of Technologies, the Dutch Academy of Arts and Sciences, the Royal Society, the American Academy of Arts and Sciences, and the National Academy of Sciences.

HERVE ARRIBART (HA) : Some articles published in the USA in 1991 presented you as a materials scientist. Do you consider yourself as such ?

PIERRE-GILLES DE GENNES (PGDG) : It depends on the period you are talking about. When we were in superconductors we did not consider ourselves as materials scientists. In fact we had a happy period when we could perform any amusing experiments, but when things became more complex we left. For instance, we had understood what vortices were doing in classical superconductors. Then there was a second stage where you should invent alloys which had special precipitates so that they would pin the vortices. That sort of action was beyond our technical means (we had very limited means in Orsay). So precisely at the moment the materials aspects became very important, we left. Clearly, with superconductors we were not in this game.
When we went to liquid crystals it was a little bit different. On the one side, there was great need of invention. Chemical invention was stimulated by the search for useful materials. In fact this case of liquid crystal was the first time I saw a molecule really built for a purpose. Bob Mayer, who was working with us in Orsay, had the beautiful idea that if you took a certain type of molecule which likes to make a tilted smectic phase, if you used a chiral molecule as a starting point, this tilted phase should be ferro-electric. And this idea came to him while queuing for lunch at the Orsay cafeteria ! He talked to us, then he came back and he induced some chemists – Patrick Keller and others – to construct a molecule like this. A few months later we had the first liquid ferro-electric. This I really look on as a landmark.

BERNADETTE BENSAUDE-VINCENT (BBV) : So would you define the materials approach as the design of molecules for a specific purpose ?

PGDG : Oui, I think that it is a clean description. There is a lot of wishful thinking where people claim that they do materials science. Often they construct objects and build molecules without knowing what to do with them.

HA : Working with chemists seems crucial for building molecules. Were there chemists in your Orsay group then at the Collège de France ?

PGDG : Yes we did have chemists in the Orsay group : Liébert, Strzelecki and Keller, three chemists. They did a lot, especially in polymerizing liquid crystals structures in order to get stable structures. They had their own lab. We had a cluster of seven laboratories on liquid crystals and they were one of the seven. At the Collège de France, when I came we had a very similar situation. For one, we had Jean Billard who was working in close cooperation with a chemist at the Collège. And Jean Jacques, who was a chemist – a great man who is dead now – took one of his best chemist coworkers – Maya Dvolastsky – and he asked her to go and work in my lab. In fact she worked for twenty years with my group.

HA : And during the superconductor period ?

PGDG : As I said during the superconductor period we were not materials inclined. We left the subject when it became materials science.

BBV : Do you think that it was the subject of liquid crystals that led you towards a materials approach or was it a more general trend in France in the late 1960s ?

PGDG : A little later when we became interested in polymers. We were stimulated by the notion that you could get some useful product. This was a time, after the 68 movement, when we began to feel that we need to be useful. For the liquid crystal project, it was intermediate. We had the notion that these materials had to be useful but we did not think that it was our duty to invent systems. We were interacting with people at Thomson who were very close – one mile from us. I had a great admiration for the Thomson research lab because they had been very active in laser research. They had a very clever advisor Pierre Aigrain, but the French activity in liquid crystals activity was not very brilliant. Looking at this time from a distance I think that had it been ten years later, we would have taken dozens of patents. At the time, the push towards application was not very strong. (I admit that we would never have invented this classical display that we have in our watches because to me it would have looked too complicated. I would have been afraid of producing the twisted system in industrial conditions. But who knows ?)
Then we went to polymers and many of us began to interact with industries. Around 1975, we really entered into an industrial network.

HA : Is there a continuity between superconductors, liquid crystals and polymers ?

PGDG : For the liquid crystals, I think we have been lucky. The Russian school had a glorious past. They could have done an immense amount of work but they did not go far enough because they had a prejudice against chemistry and dirty materials. Because of that we could set up a French activity on liquid crystals without having Russian competition. It was a great luck.

HA : However you were not an advocate of dirty science ?

PGDG : The tradition of superfluidity was very clean. The materials we were using were model materials with few defects. When Anderson used the word “dirty superconductors” he meant alloys. It is true that the physics of alloys has been very different for superconductors from the physics of pure metals. You can reduce the correlation length, you can control it by choosing the mean free path. There are many facets that become available when you accept to work with alloys. But in my mind, these alloys were perfect alloys without any precipitation or any complicated effect. They were ideal materials, although Anderson used the term dirty alloys (for provocative reasons).

BBV : Could you please clarify YOUR notion of dirty material ?

PGDG : I don't use it often because in many cases there is a prejudice. My own distinction would be slightly different. It would be between universal and zoological. Let's take a different field, like interfacial science : you can find universal features in this. You can construct general laws. The statics and dynamics of wetting are also pretty universal. But if you have a very specific problem such as making a polymer hydrophilic on its surface, then you enter into a certain amount of zoology. For instance, to create a hydrophilic surface by a plasma treatment, this plasma treatment works in an unknown fashion with empirically chosen gases, under conditions that are not deeply understood. Details on a chemical surface are not universal, and when you work for a practical purpose, you better go into these details. Our attitude as physicists was to start from the universal features… with the hope that it would be useful for applications later.

HA : This is a physicist's perspective. But when dealing with polymer materials you had to extract some cleanness out of dirty stuff.

PGDG : It is true that there is a huge conceptual gap between semiconductors where you look for impurity fractions which are amazingly small and polymer physics where in all cases you will synthesize a polymer by a process which has some randomness. However, you can build up universal laws despite the intrinsic distribution and complexity of these materials.

HA : What lead you to soft matter science ?

PGDG : There is an amusing historical aspect. We had been working on superconductors when one day we had a beautiful seminar by Charles Sadron, one of the founders of polymer science in France. He started from polyethylene (that we suck when we suck milk from a bottle) and moved to considerations on DNA. He covered everything, in this wonderful talk. Our little group in Orsay was fascinated by his talk and we decided to go that way. Sadron's lab (then directed by Henri Benoît) was brilliant not only in science but also from the human aspect : they accepted us coming with our questions sometimes relevant and often stupid. They really established a co-operation with us. We worked for two or three years on polymers (it was roughly in 1966). We produced some little theoretical reflections on the dynamics of chains in solutions. But we didn't have an experimental lab with us in Orsay. This situation of hanging on theory exclusively, I did not like it. In 1968 or ‘69, we heard about liquid crystals by Georges Durand. He came back from the US and told us it was something for the future. We listened to him. So we suddenly shifted from polymers to liquid crystals and we worked on it for about 5 years. It was a happy period because within a few months when we crystallized the idea we got seven independent units cooperating on this project. There were chemistry, as I mentioned, nuclear resonance, defects (Friedel was very helpful because there was a tradition), optics, theory, and crystallography. I may forget some of them but it came up to a bunch of six-seven groups working together in a happy way. Funding was easy. These groups were not nervous about their future ; they were very open and willing to go into something like that. It was a great time to connect all these good people and just working together. The results were obvious. Within two or three years there was a French science on liquid crystals. There had been one fifty years before with Georges Friedel. But there had been a gap with only one group flying the flag energetically, the Chatelain group in Montpellier. They were lonely, however. They had a good education in liquid crystals but many tools that were obvious to us - such as inelastic light scattering, or nuclear magnetic resonance - were unknown to them. So to come back to our point, we in Paris could set up something very efficiently in a short time and one of our sources of pride was that it cost no extra money to the taxpayer. Because all the equipment was already there, there was no new costs.

BBV : You mentioned that you took advantage of the large apparatus in Orsay…

PGDG : Not big. It was not synchotron or reactors, no large machines.

HA : And neutron scattering ?

PGDG : There was some neutron scattering on liquid crystals but it was minor. X rays yes ; we used a lot of x rays especially when we came to the more zoological work with a long list of smectic phases which are more and more complex. But no large apparatus.

HA : When you began on polymers was there a lot of experimental data from neutron scattering ?

PGDG : We came back to polymers after liquid crystals. I was at the Collège de France. We established a three-group collaboration with Strasbourg (Henri Benoît, a leading figure) and a group with Gérard Janninck at Saclay on neutron scattering. Here neutron scattering was very helpful to examine the conformation of one chain in a dense system where there are many other chains. If you have isotope labeling you can have this chain labeled, and you look at this chain and describe the conformation of one particular chain. In that case, there was an old prediction by Paul Flory that this chain would behave like an ideal random walk – which is surprising for a strongly interactive system. Indeed the Janninck group proved that this was the case. So we had this cooperation, we were what we call in French "la mouche du coche", a little fly stimulating the carriage but we had very little meat. Gradually however we got some. Francis Rondelez installed clever optical techniques. At the Collège at that time we had two types of activities : one was polymers, the other one being surfactants. It was the time when young group leaders became advisors in industries. Christiane Taupin, who worked on surfactants, went to Levallois to head a group of Atochem. Francis [Rondelez] was an advisor to Elf, and I was an advisor to Rhône-Poulenc. We worked more and more in close connection with industry. This was another happy time also based on cooperation. However it was a different cooperation, no longer a federation of little groups but a cooperation of large units, like Strasbourg. In Strasbourg they had a culture in light scattering and H. Benoît had constructed very detailed descriptions based on light scattering. Suddenly they were given the neutron scattering with isotopes providing information at a smaller scale (50 Ångströms instead of 5000). They were immensely happy with the neutron and Benoit wrote a book about neutrons and polymers.

HA : Nevertheless you spoke in critical words about big instruments.

PGDG : That was later. From the 1960s to 1985, I was a supporter of them because they had an educational aspect. This may be specific of European countries which have been delayed by the war. In the provinces, France had excellent abilities but no education. If you took young scientists from the lonely sites and brought them to Grenoble or to Saclay they learnt very fast in this intense research milieu using many concepts they had never heard about. They came back to their own labs and brought what they had learnt. So it was immensely useful. I think that the early generation of big machines has been excellent. At this moment, I am less enthusiastic because the educational problem has been solved, fortunately. A student in a small city in France can have a good education in basic physics of condensed matter. From the point of view of discovery, the density of discoveries around big machines has dropped down fast. Let me take an example. Going back to the far past, in 1957 (the year when the Russians launched Sputnik), at the first international conference that I attended as an engineer at the CEA in Stockholm. It was about neutron scattering. I learnt two things from this meeting : I heard a talk by Harry Palevsky, a student of Fermi. He was an invited guest for six months in Stockholm. He had worked on the very small Stockholm reactor using energy selection methods which are very primitive – it was just a beryllium filter : it does not provide a peak in energy, just a step. Using only that, he has been able to study the protons of helium. That was beautiful ! It taught me in some sense that you could work with simple means without big machines. The second thing I learnt was the danger of theoretical gurus. There was a number of them at this meeting, in particular Walter Marshall and Roger Elliott from England. I was just a PhD student. I came and said to Roger Elliott that he wrote something wrong in a review article. He pushed me out although he was wrong. That taught me some caution with the old gurus.

HA : Let us come back to adhesion. It was a good example of a dirty problem at that time based on some science and on empirical rules.

PGDG : You are absolutely right. We entered into adhesion after spending some time on wetting, which is more fundamental. I was struck by the great chemical successes achieved in adhesion. The example that I often quote is anaerobic adhesives. These are systems that you want to reticulate, to polymerize once they are in a proper position between two walls but you don't want them to react stupidly in other situations. In that case, chemists were able to have a polymerization induced only in the presence of certain metal surfaces like copper. That is chemical invention. My impression is that chemistry has been the leader in this field. We physicists, and the people from mechanics, we were in a more modest position. People from mechanics brought measurements. To define adhesion properly instead of measuring the force between two pieces, Griffith and others established that you have to measure the separation energy per unit area. So people from mechanics provided 1) measurement techniques like the cantilever technique and 2) new concepts. Thus, chemistry ranks one, mechanics two, and physics comes only as number three.
So in adhesion meetings you could hear these nice theoretical talks – not easy theory indeed – but very nice. At the end of such talks somebody raised his hand and asked : “what does it tell me about this particular adhesive where I found that when I modify my molecule by putting this methyl group in the sixth position I get a much better adhesion than if I put it in the fourth position ?” So that was a kind of Babel Tower. Our modest aim was to try to build up a common language. We helped a little bit in two respects. One is the question of very soft adhesive materials where dissipation inside the adhesive is what makes a material good. We could help because it was close to concepts we had met in polymer science. The other question concerns little polymer chains that intertwine. Liliane Léger has been working on it. We thus had, let's say, two years full contribution but it was very modest. It did not clarify the science of adhesion. But it helped create a number of teams in France. If you look at the situation I would say we have :

1) a classical lab in Mulhouse where modern physics was introduced by Günther Reiter ;

2) Costantino Creton here in PC [the École Supérieure de Physique et de Chimie Industrielles] ;

3) Liliane Léger on polymer systems at the Collège de France ;

4) a small group with M. Shanahan in Corbeil.

HA : Apparently it took time for you to convince them to work on such a subject.

PGDG : Absolutely right. My dream would have been to set up a sort of adhesion science center in the Paris area. Ultimately I did not manage to do it. There are various scattered researches but no unity although it is not too bad.

BBV : Did you work on adhesion because you had industrial contracts or was it your own initiative ?

PGDG : I think it was our own initiative, although I may be wrong because it is very difficult to trace the origin of a project. We had no program with 3M, the great master in industrial adhesion. Rhône-Poulenc had some related problems but they don't sell adhesives as such. Latex is special : it is not a real adhesive. We heard about adhesives but it was not something important for them.

HA : And Gilbert Schorsch from Rhône-Poulenc ?

PGDG : He was more concerned with new materials, organo-mineral materials. Later they turned to adhesives. I don't remember well. I think that the wetting problem, dealing with interfaces led us to move to strongly interacting systems. But we should be very modest. Take for instance a standard adhesive material like the epoxy-glue that you buy in a supermarket. Frankly, I don't understand the way it works.
We are still working on adhesives. If you look at this blackboard here (Figure 1) you'll see that recently we have been concerned with cellular adhesion. We have a professor in medicine in Marseilles, Pierre Bongrand, a former student in a solid-state graduate school here in Paris, who brought a number of key measurements in adhesion.

Figure 1. Cellular adhesion schema

The notion is of a cell with a few sticky molecules at its surface but they are very small, very dilute. When the cell comes in front of another one, all the sticky molecules move to the contact region and build up bridges there. Ten years ago Bongrand and others understood the statics of that process and what the separation energy is. It is not at all what stupid people like me would have believed. When you begin to separate you do not have to cut a bond because all the stickers just go to a smaller surface but they don't disrupt their bonds. So the adhesion energy is just fighting against the osmotic pressure. People like these established deep ideas about the statics. While I had to give a course I realized that there was a cascade of problems concerning the dynamics and I started thinking about them. So we are still on adhesion.

HA : How do you see the links between biology and materials research ?

PGDG : I have been very critical about biophysics. For instance, physicists had in mind that they could do a lot of biophysics on cellular adhesive molecules by establishing the 3-dimensional structure of these proteins. It is helpful. However, it is not a very exciting program because the biologists are so clever that they immediately sequenced these proteins. They realized some parentages between the sequences, grouped them into families and could identify the function of the various pieces without a big instrument of physics. The interesting problems – how does it work in a tumor situation, or how do I influence this process, how do I stimulate them – are not in biophysics. Biophysics is doing only the details, not addressing the big question. That is why I have been so critical of this community who jumped into biophysics at one stage. Fortunately, I was partly wrong. There are good examples around here : at the Institut Curie Center with Jacques Prost, they really have a wonderful activity. For instance, they have a universal theory of molecular motors. That is a real success of biophysics. There are facets of biophysics that I respect very much but there are still old facets that I would call more engineering than science.

HA : Let's talk about the artificial muscle.

PGDG : The subject was started by a giant in polymer science, Katchalski. Polymer physics started with Kuhn in the 1940s. Ten years later Katchalski, a former student of Kuhn, said : “if we understand rubber, maybe we can devise a rubber or a gel where a chemical agent changes properties, transforming chemical energy into mechanical energy”. That was a beautiful idea. Katchalski did very sophisticated work with very simple means. He had very few materials available in Israel at the time : he used methylacrylate recuperated from the cockpit of World War II aircrafts. He did a wonderful job. The materials he produced demonstrated the principles but they could not have any practical application because of slow response and fatigue problems. This historical contribution raised an interesting challenge.
We started as a small thing. With gels, the response time was very bad. Then we tried liquid crystals systems with no solvent. You just changed the temperature to switch the conformation. That was tempting. So we have a project at the Institut Curie which requires delicate chemical synthesis. Another project was launched by a Japanese team in Osaka. They are electrochemists and they used a membrane made of a popular material for other purposes in large-scale electrochemistry. This membrane is called a Nafion ; with this Nafion they were able to achieve systems that under moderate voltage – a few volts – distort and then command actions. The response time was around one second. I am full of admiration : not only did they build up the material with the correct (large-area) electrodes but they also understood the dynamics of the process. The field is very attractive (but our contribution is very, very small).

HA : Would you say that artificial muscle is a bio-inspired material ?

PGDG : It is not really bio-inspired. It is based on polymer science and has nothing to do with an actual muscle. But I am fully convinced that bio-inspired materials will become more and more important. I was very impressed by the German team that found what are the peptides at work in making the shell of diatoms. Using this sort of results in the future is very tempting.

BBV : Did teaching play a part in your continuous shifts from one project to another one ?

PGDG : Ah oui, teaching played an important role. This figure on the blackboard on cellular adhesion really came from the fact that Françoise Brochard was having a course on soft adhesives for industrial people. When she asked me to talk about cellular adhesion I just realized that I could not teach it because I did not really understand the process involved. So it was an excellent push. Teaching is very helpful for theorists because we are often trapped in formal models. Mathematical writing does not give any idea of the real thing. We have to re-digest and transform the mathematical statements into a few simple sketches without any calculation. Teaching is good for going in this direction.

HA : What about your experience as a Director of an engineering school ?

PGDG : I have tried to keep scientific contact with the labs, on gels, on separation techniques and some other cases. I try to keep this place aware of new fields and to keep good contacts with local people. I sometimes missed the point because of too many duties, but right now I am very happy. We have new young professors such as Jérome Bibette working on emulsions, Ludwig Leibler on polymers, Jérome Lesueur on transport in superconductors and it is very stimulating to talk with them. The person you really want to direct such a place is somebody who is able to talk to everyone. I would be scared to have separate departments for physics, chemistry and biology.

BBV : Do you think that throughout your career you crossed disciplinary boundaries, or are you still a physicist but able to talk to other disciplines ?

PGDG : I tend to see it more as a process of learning. For instance when we entered the field of polymers we were like students. As I said, we made many mistakes. Our lives have been a cascade of student lives. At least this has been my feeling. For the theorists it is easier to move, they can switch more easily than experimentalists. But some experimentalists did switch : Etienne Guyon for example moved from superconductors to liquid crystals and granular matter. He is an interesting case.

HA : Do you intend to pursue your recent interest in glass ?

PGDG : The literature is difficult to grasp. We look at a certain sector, mainly on structural glasses, with problems in real space, numerical local space features.

Fin de l'enregistrement

Pour citer l'entretien :

« Entretien avec Pierre-Gilles De Gennes », par Bernadette Bensaude-Vincent et Hervé Arribart, 2 mai 2002, Sciences : histoire orale, /spip.php ?article59.

Pour citer l'entretien :

« Entretien avec Pierre-Gilles De Gennes », par Bernadette Bensaude-Vincent et Hervé Arribart, 2 mai 2002, Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article59.

Lieu : bureau de Pierre-Gilles De Gennes, Ecole Supérieure de Physique et de Chimie industrielles, Paris, France.

Support : enregistrement sur cassette.

Transcription : Bernadette Bensaude-Vincent, Hervé ARRIBART.

Édition en ligne : Sophie Jourdin, Sacha Loeve.